Threaded pipe or rod strings are used in horizontal installations for trenchless technology applications, particularly pipe bursting. High tensile loads are applied to pipe strings which pull bursting tooling through existing pipelines to facilitate replacement with a new product pipe. During push-out, the process of assembling the rod string from individual rods and pushing the assembled string through an existing host pipe takes a modest amount of thrust. During pullback, the portion of the process wherein the pipe is cracked and the surrounding soil is expanded, the load will be higher than during push-out. Variation in job size, host pipe material and adjacent soils all affect the maximum tensile load applied to the rod string.
To produce the tensile and thrust loads on the rod string, multiple hydraulic cylinders are often used as they provide an efficient means for producing large loads. These cylinders are part of a downhole device used to thrust, pull, assemble and disassemble said rod string. Further, these cylinders are actuated by hydraulics delivered by a hydraulic pump, most often turned by a gasoline or diesel engine.